Is the ETranslate translation SEO friendly?

Yes. After adding a language to your store, a locale-aware URL is generated automatically. For example, you have added German as an additional language, you can view your store in Germany by loading the following URL: https://yourstorename.myshopify.com/de. The "hreflang" HTML meta tags are also added to the store website, so they are indexed properly with search engines (Google, Bing, etc).